I actually find the $100 price gap between the iPad Air and iPad mini with Retina palatable since the only difference between the two is size. Last year, the iPad Mini was a miniaturized version of the then 18-month old iPad 2 (A5+512MB RAM). This year, the Air and rMini have the same CPU and RAM. They're basically the same machine in different form factors.
If you think the full-size iPad Air is worth $500, why is the retina Mini not worth $400? By my guess, actual manufacturing cost difference between the two models is around $50 (for display and battery).
That said, I'm currently enjoying my Nexus 7 (2013) LTE.